This invention relates to the preservation of minimally processed fruits and vegetables and flowers, particularly cut and peeled or juiced fruits and vegetables.
Most fruits and vegetables are subject to discolouration and spoilage once they are cut and peeled. This is usually due to enzymatic and bacterial action.
Patent application WO 97/16976 discloses a method of storing cut apple pieces in which whole apples are washed in chlorinated water to inactivate microorganisms, the apples are then cored, peeled and sliced and immersed in an ascorbic acid solution having a pH of 2.2 to 2.7 and are then drained and stored in modified atmosphere containers.
Patent application WO 99/34683 discloses a method of treating cut fresh vegetables by dipping in a solution containing calcium ions and ascorbate or erythorbate ions.
U.S. Pat. No. 6,054,160 treats cut apples with a solution containing L-cysteine, sorbitol, and calcium chloride and then stores them in a modified atmosphere pack.
These treatments provide a shelf life of up to 2 weeks but in practice this is not long enough.
It is an object of this invention to provide an improvement in shelf life for minimally processed fruit and vegetables.
To this end the present invention provides a process of extending the useful shelf life of minimally processed fruits and vegetables which includes the step of treating the fruits and vegetables with a flavonoid compound.
This invention is partly predicated on the discovery that the presence of flavonoids inhibits the enzymatic and bacterial action that leads to discolouration and spoilage. The flavonoid may be added to a solution sprayed or dipped on to the processed fruits or vegetables or added to the fruit or vegetable juice.
Flavonoids such as proanthocyanidin have been identified as antioxidants and recommended as food additives for nutriceutical use but not to prevent deterioration in minimally processed fruits and vegetables.
It is preferred that an anti oxidant such as ascorbic acid, erythorbic acid, lipoic acid including alpha lipoic acid, be present with the flavonoid compound. It is believed that these compounds act synergistically with the flavonoid compounds to inhibit oxidation of the minimally processed fruits and vegetables. Some fruits and vegetables have an adequate content of ascorbic acid and for these addition of a flavonoid is sufficient.
Throughout this specification minimally processed means the steps of processing raw, uncooked fruits, nuts and vegetables for storage and/or transport prior to eating or further processing. This includes peeling, coring, slicing and juicing.
Throughout this specification flavonoid means a polyphenol compound of the type having at least two aromatic rings which occur widely in the plant kingdom and inhibits oxidation. These compounds may also form polymeric compounds with the flavonoid repeating unit. The term flavonoid as used throughout this specification includes individual flavonoids, mixtures and plant extracts having a high flavonoid content.
The fruits to which this invention is applicable include oranges, mandarins, grapefruit, tangerines, tangellos, pomellos, kiwi fruit, mango, pineapple, apricots, strawberries, blackberries, raspberries, mulberries, cherries, blueberries, grapes, figs, peaches, nectarines, apples, pears, nashi, plums, tamarillo, cantaloupe, guavas, lychees, rumbutans, melon, passionfruit, avocado and mangosteen. Nuts such as chestnuts may also be treated.
The vegetables which can be treated according to this invention include broccoli, brussel sprouts, carrot, cabbage, capsicum, chili, chocos, cauliflower, celery, lettuce, garlic, ginger, green beans, shelled peas, asparagus, corn, pumpkin, mushrooms, snow peas, zucchini.
The fruit or vegetables are sprayed or immersed in the solution containing the flavonoid and excess solution is removed from the surfaces and the products are packaged in the usal way for minimally processed fruits and vegetables.
Fruit juice can be preserved by the addition of flavonoids to the juice. Navel oranges are usually not preferred for juicing because the juice acquires a bitter taste. The addition of a flavonoid to navel orange juice inhibits the development of this bitter taste. In preparing the fruit juice the pulp is usually separated from the serum and then recombined to form the juice. The flavonoid may be added to either the pulp or the serum or both but preferably to the pulp.
In another aspect of this invention the present invention provides a preservative composition for use in preserving minimally processed fruits and vegetables which composition includes a flavonoid mixed with a food grade anti oxidant, preferably selected from one or more of ascorbic acid, erythorbic acid, lipoic acid including alpha lipoic acid and salts thereof such as sodium, potassium and calcium ascorbate. This is preferably a powder but may be a liquid concentrate that can be diluted in water, tea infusion or a fruit juice to form the dipping solution. The ratio of flavonoid to antioxidant is usually from 1:50 to 1:150 by weight. This mixture is then diluted in 30 to 50 times its weight in water or fruit juice. The flavonoid content in the dipping solution or in juiced fruit or vegetable is preferably from 0.01 wt % to 0.1 wt %. In addition to the flavonoid, alpha lipoic acid may also be added to the dipping solution or fruit or vegetable juice as an additional antioxidant in amounts from 0.0005 wt % to 0.005 wt %.
The flavonoid may be any available compound or extract. The group takes its name from the compounds flavone, flavonol, flavanone but also includes chalcones, anthocyanidins, proanthocyanidins, isoflavonoidsand polymeric forms of these compounds. Flavonoids are available as plant extracts and are an effective source for use in this invention. A preferred flavonoid source is an extract from pinus radiata or pinus pinasta [maritime pine] marketed as Enzogenol(trademark) and Pyncogenol(trademark) respectively. Enzogenol contains about 38% polymeric proanthocyanidins, 25% oligomeric proanthocyanidins and 22% monomer, dimer and trimer proanthocyanidins. Grape seed extract and grape seed oils are another favoured source. Also may be mentioned Quercitin, a flavonoid present in grapes, apples, broccoli and onions, acerola from cherries, hesperidin, rutin and any plant extracts rich in flavonoids such as citrus seed extract, cranberry extract, juniper berry extract, rose hip extract.
The dipping or spraying solutions may contain other ingredients for flavour and to assist the action of the flavonoids. Acid to maintain a low pH for antibacterial effectiveness is a useful ingredient and any food grade acid such as citric acid may be used. Alternatively acidic fruit juices, such as pineapple juice, may be used. Other ingredients may include sugar, water sanitisers such as colloidal silver, or microhydrin.